perpend is right! In this case 'etwa' has the meaning of 'vielleicht'.
'etwa' is one of many flavoring particles in German that can change the meaning, or at least the undertone, of the whole sentence.

Wiki knows this about it.
It's a bit of an advanced topic for a non-native speaker, so don't get frustrated by the many different meanings these filler words can have within different context. It will take time to get used to them.